Addition of silica powder, colloidal silica or the like to organic resin compositions is widely known as a means to improve abrasion resistance, staining resistance, solvent resistance, water resistance and the like of cured resins.
Aqueous colloidal silica in which water is used as its dispersion medium may be used for the production of a colloidal silica-containing organic resin composition, but other forms of colloidal silica in which dispersion media other than water are used (what is called organosilica sol) may be used more preferably because such organosilica sol has high compatibility with various components in the organic resin composition in many cases.
Every type of the prior art organosilica sol is produced by merely using an organic solvent as its dispersion medium. Japanese Patent Application Kokai No. 63-305176 discloses that, by coating such an organic resin composition containing the organosilica sol on a transparent plastic or glass base, a cured resin suitable for optical purposes can be obtained because of the composition's ability to improve abrasion resistance, dyeaffinity and the like of the resin.
However, such organosilica sol which is prepared by merely replacing its dispersion medium with an organic solvent cannot be used in a solvent-free reaction system (bulk-polymerization), because the organic solvent is generally distilled off after the addition of the organosilica sol to a monomer system for resin use or to a resin composition. In addition, the organosilica sol is apt to undergo an influence of compatibility of its dispersion medium with other components in a resin composition, thus easily resulting in the flocculation of silica particles.
Recently, new techniques for the dispersion of silica particles in dispersion medium other than water have been developed, in which the surface of colloidal silica particles is reformed with organic compounds beforehand.
For example, Japanese Patent Application Kokai No. 49-126594 discloses a process for the production of an organosilica sol in which aqueous colloidal silica is esterified with a water soluble alcohol and the thus esterified silica sol is again subjected to esterification with another alcohol which is hardly soluble in water. Also, Japanese Patent Application Kokai No. 2-64138 discloses a polymerizable silica sol which is produced by firstly reacting aqueous colloidal silica with an alkoxysilane compound having polymerizable unsaturated double bonds to introduce the polymerizable unsaturated double bonds to the water dispersion type colloidal silica particles and then replacing the dispersion medium with an organic solvent.
A number of techniques have been developed for the incorporation of silica into a cured resin as a component of the resin, by allowing colloidal silica to react with an organic resin composition during its curing step.
For example, Japanese Patent Application Kokai No. 53-11951 discloses a process for the production of an organic resin material for industrial use having proper hardness, non-combustibility and the like, which is produced by copolymerization of an alkyl silicate with an organic polymer containing hydroxyl and carboxyl groups in its molecule, especially with an acrylic copolymer. Also, Japanese Patent Application Kokai No. 59-71316 discloses a coating composition useful for the formation of a film having excellent durability and staining resistance, which comprises a resin as its main component obtained by copolymerizing colloidal silica with an .alpha.,.beta.-monoethylenic unsaturated carboxylic acid alkyl ester or the like and with a silane-based monomer compound (silane coupling agent). According to the aforementioned Japanese Patent Application Kokai No. 2-64138, a curable composition for coating use is disclosed which comprises the polymerizable silica sol prepared in the aforementioned manner and a monomer containing other polymerizable unsaturated double bond and which forms a cured film having excellent abrasion resistance and solvent resistance when cured by means of ultraviolet rays, electron beam or the like.
It is known that a polymer having excellent heat resistance, water resistance and optical properties can be obtained by polymerizing a (meth)acrylate having an adamantane structure, alone or with other acrylate monomers. The following describes examples of (meth)acrylate monomers having the adamantane structure.
According to Japanese Patent Publication No. 46-28419, an adamantane mono (meth) acrylate represented by the following general formula ##STR1## is produced from adamantane monool and (meth)acrylic acid. A polymer or a copolymer is obtained from this adamantane mono(meth)acrylate by its polymerization with the aid of a radical initiator or light exposure.
Also, In Japanese Patent Publication No. 63-22205, a diallylester derived from an adamantane carboxylate is disclosed.
Polymers prepared from these prior art adamantane mono(meth)acrylate and diallylester have excellent heat resistance and optical properties. These polymers, however, have disadvantages such as poor workability due to their excessive hardness and poor adhesion ability to other materials.
Because of these reasons, development of new derivatives having an adamantane structure have been called for in the related fields. In addition, virtually nothing is known about a silica sol in which a (meth)acrylate derivative or the like having an adamantane structure is used as dispersion medium.